1. Field of the Invention
This invention relates to cold flow additives for middle distillate fuels which improve the flowability and filterability thereof at low temperatures.
In geographical areas which experience severe winter weather, users of middle distillate fuel oils, especially diesel fuel, have encountered problems caused by water droplets entrained in and wax separation from said fuel oils at low temperature. This wax and water, the latter in the form of ice crystals, clog fuel lines, strainers and filters preventing and/or restricting the flow of said fuel to apparatus or engines designed to utilize the fuel. In extremely cold weather, solidification of middle distillate fuel in fuel tanks and lines occurs, because when a wax-containing oil, for example, a middle distillate fuel oil, is cooled it will eventually congeal due to the precipitation of wax.
Additives have been used in the petroleum industry for many years to improve the low-temperature properties and characteristics of petroleum-derived middle distillate fuels. These additives, commonly termed cold flow improvers, wax crystal modifiers and/or pour point depressants act by changing the morphology of wax crystals, reducing the pour point of said fuels and by reducing or preventing the formation of ice crystals from water entrained in the middle distillate fuel (i.e., anti-icing agent).
The major influence of cold flow additives for middle distillate fuels is in reducing the size and shape of wax and/or water crystals, i.e., ice, and their tendency to form a fuel trapping matrix. These additives effectively lower the pour point of the fuel and enhance its low temperature flow properties.
2. Description of the Prior Art
The use of additives to impart desirable physical and chemical properties to middle distillate fuels during cold weather is known and appreciated by the prior art.
For example, U.S. Pat. No. 4,211,534, to Feldman discloses a three or more component additive system for distillate fuel oils which consists of (1) an ethylene polymer or copolymer, (2) a second polymer having alkyl side chains of 6 to 30 carbon atoms, derived from carboxylic acid esters and/or olefins and (3) nitrogen compounds, such as amides, amine salts and ammonium salts of carboxylic acids or anhydrides. the additives are described as useful in improving the cold flow properties of distillate hydrocarbon fuel oils.
U.S. Pat. No. 4,113,442, to Hoff et al. relates to middle distillate compositions which contain a filterability improver which consists of a mono- or polyester of a specified C.sub.10 -C.sub.40 hydrocarbyl alcohol and a hydroxycarboxylic acid. These compositions may contain small amounts of unreacted alcohols or of fully or partially unconverted alcohols. In addition, the composition may contain a pour-point depressant.
Suitable pour-point depressants include copolymers of ethylene and vinyl esters, alkylacrylates, alkylmethylacrylates or alkylfumarates, chlorinated polyethylene, alkylated aromatics alkylated polystyrene, fully or partially hydrogenated polymers or copolymers of olefins, for example butadiene or mixtures of butadiene and styrene, and, polyalkylacrylates or methacrylates and mixtures thereof.
Another cold flow additive for middle distillate fuels is disclosed in U.S. Pat. No. 4,058,371 to Ilnyckyj, which discloses an oil-soluble, alkphatic copolymer suitable for use as a nucleator for wax crystallization, in combination with an oil-soluble derivative of an aromatic copolymer. Ethylene-vinyl acetate copolymers having an average molecular weight of from 500 to 50,000 are described as desirable nucleators for wax crystallization.
U.S. Pat. No. 3,910,776, to Feldman, relates to cold flow additives for distillate fuel oil which consists of combinations of (A) alkyl aromatics consisting of the condensaton product of chlorinated wax and naphthalene, with (B) ethylene containing copolymers and/or (C) N-aliphatic hydrocarbyl succinamic acids and their amine salts.
U.S. Pat. No. 3,380,815, to Herbst, discloses a cetane improver for diesel fuel oil which consists of adding a small amount of a gem dinitrolalkanoate to a diesel fuel. The gem dinitrolalkanoate is prepared by the base-catalyzed condensation of a dinitroalkane and an .alpha.-.beta.-unsaturated ester.
From the foregoing, it can be seen there is an ongoing search for cold flow additives suitable for use in combination with middle distillate fuels.
It is a principle object of this invention to reduce or prevent the formation of wax and ice crystals in middle distillate hydrocarbon stocks at low temperatures.
It is yet another object of this invention to increase the cetane number of middle distillate hydrocarbon stocks.